This type of mixer is known from DE-U-299 11 066. The known mixer contains a mixing screw which comprises a single spiral which is wound in a screw shape around a screw shaft. The spiral terminates in the lower section of the screw shaft with a take-up edge. The known mixing screw is furthermore provided with a short secondary blade, which is formed similar to another, but shorter spiral which extends from a minimum of 20° to a maximum of 360° around the screw shaft. The secondary blade is provided with a take-up edge which is arranged offset by 180° to the take-up edge of the actual spiral. The width of the secondary blade in the radial direction is a maximum in the region of the take-up edge and reduces continuously and prominently to zero with increasing distance from the take-up edge. The purpose of this secondary blade is to smooth out the discontinuous discharge of the mix, as observed with mixing screws with a single spiral, through the discharge opening, whereby the maximum amount of mix is always then output when the take-up edge of the spiral passes the discharge opening and whereby the amount of the discharge mix is then again substantially reduced. The object of the construction of the known mixing screw incorporates the idea that by arranging a second take-up edge two maxima in the mix discharge are obtained. This result is however not satisfactory.
Mixing devices with mixing screws are also fitted with the most varied additional equipment. For example, U.S. Pat. No. 5,456,416 shows a mixer in which the lower section of the mixing screw is extended radially outwards, as a type of blade, whereby the leading take-up edge is located exactly on the radial line to the rotating axis. A deflection plate is mounted on the upper side of the extended part to guide the mix in the direction of the rotating axis.
U.S. Pat. No. 5,590,963 shows a feed mixer which is fitted in the lower section of the mixing screw with three evenly spread pushing or smoothing blades. The blades are arranged with the outer sections of their take-up edges trailing and comprise a narrow, strip-type of design so that also nothing can be deposited here.
A similar construction is shown in U.S. Pat. No. 5,647,665.
U.S. Pat. No. 3,997,146 shows a feed mixer, the mixing screw of which is fitted in its lower section again with two strip-shaped scraping elements extending outwards, the edges of which run radially to the rotating axis.
GB-A 2 310 793 describes a feed mixer, which comprises a large number of different elements on the lower section of the mixing screw. For example, the mixing screw includes a strip-shaped carrier, the leading edge of which runs radially, and the upper side of which is fitted with blades. Furthermore, a paddle is fitted, which is joined to the rotating axis on an arm which is narrow in the circumferential direction. The paddle is formed constructively such that the mix dropping down in the vicinity of the boundary wall of the mixing chamber is pressed upwards, increasing the density of the material in this section.